Historically, the manufacturing of parts from raw stock or material has involved two distinct, albeit combinable, manufacturing processes. Fabricating a part through subtractive manufacturing (SM) involves progressively removing or machining material from raw stock until the part has been reduced to a rough form within a specified tolerance. In SM processes, raw material is often removed by turning, drilling, or milling the part being fabricated. Drilling involves traversing a rotating bit along a longitudinal axis while milling operates in three-dimensional space. Following completion of SM processes, post-processing may be required to smooth, polish, finish, or otherwise transform the part into final completed form.
Fabricating a part through additive manufacturing (AM) involves progressively adding or depositing material onto a part being fabricated, often by adding successive layers, until the part approximates an intended shape and size. However, in contrast to SM, many AM processes add support materials or scaffolding to the part being fabricated as part of the AM process plan, so that the part does not collapse under its own weight because the part being fabricated will continually increase in size and weight as manufacturing progresses.
While SM processes often end when a rough form of the desired part has been achieved, AM processes may instead create a shape that still requires further transformation due to the addition of the scaffolding. This interim result is known as a near-net shape, which is the part being fabricated, plus any supports that were added during AM manufacturing. Ordinarily, the near-net shape is post-processed to remove the scaffolding using a range of potential processes from manually removing the supports with a chisel-like cutting tool to programming collision-free tool paths for a CNC-mill to remove the supports, after which even further post-processing may be required to transform the part without scaffolding into final form.
Due to the need to remove scaffolding, AM can be characterized as one of several manufacturing processes that may be needed to fabricate a part, rather than as a stand-alone solution, although removing scaffolding is but one example of a manufacturing process that involves both AM and SM operations. More generally, any sequence of AM and SM processes, independent of the ordering of their respective contributions, can be defined as a hybrid manufacturing process. An approach to process planning for hybrid manufacturing is described in U.S. Ser. No. 15/858,677, filed Dec. 29, 2017 the disclosure of which is incorporated by reference.
In a hybrid manufacturing process, understanding the interactions between SM and AM operations is critical, especially when planning the layout and removal of the supporting material generated by the AM process. The interaction of SM and AM processes creates a spatial planning problem that requires the analysis of the feasible, that is, non-colliding, spatial configurations of tools to be used against a dynamic near-net shape that must be continually updated whenever a support is removed. The analysis also requires determining whether supports are being placed in locations during AM that will later be inaccessible to the cutting tools used in the SM process.
Hybrid machines equipped with both AM and SM capabilities have emerged, including the Ambit™-Dextrous Manufacturing system, sold by Hybrid Manufacturing Technologies, McKinney, Tex., and the Lasertec 65 3D, sold by DMG Mori Seiki Co., Nakamura-ku, Nagoya, Japan. These machines typically couple a LENS (Laser Engineered Net Shaping) or similar direct energy deposition AM process with a high-axis milling center to enable AM parts fabrication on curved surfaces. However, LENS-type AM processes are not well suited to creating near-net shapes, which limits the range of parts that can be built.
Therefore, a need exists for an approach to planning removal of AM-process-generated supports from a dynamic near-net shape through an SM process.